1. Field of the Invention
The present invention relates generally to reproduction apparatuses and methods capable of starting to reproduce compressed video images, music and other similar information, and particularly to reproduction apparatuses and methods capable of starting to reproduce information at a designated reproduction start time point.
2. Description of the Background Art
In recent years, digital versatile disk (DVD) is increasingly used as an optical disk capable of storing a variety of information such as motion video and music.
To allow video images, sound and the like of longer periods of time to be reproduced, DVD and similar storages media have recorded therein audio, video and/or other similar information encoded (or compressed), i.e., encoded data (hereinafter referred to as “compressed data”). The compressed data is divided into units of data each referred to as a packet having attached thereto timing information employed when the data is reproduced (or decoded). This information is referred to as a “time stamp”.
When a user reproduces music, a video image and the like stored in a storage medium, the user often reproduces it at his/her desired portion. Accordingly, most reproduction apparatuses have a function effecting a time search process to obtain a position at which the information to be reproduced starts, as corresponding to a start time point designated by the user.
Apparatuses and methods associated with the time search process have conventionally been proposed. For example, Japanese Patent Laying-Open No. 2004-213728 discloses a DVD reproduction apparatus and method that can employ a time of reproduction of a cell included in program chain information to search for a reproduction position corresponding to a designated time.
Furthermore, Japanese Patent Laying-Open No. 2000-173248 discloses a time acquisition method that acquires from a pack of digital audio data a presentation time stamp (PTS) controlling a time point for reproduction, and also acquires a track's reproduction start time point and total reproduction time from management information to calculate the current reproduction time point and remaining reproduction time.
Furthermore, Japanese Patent Laying-Open No. 2003-228964 discloses a search method storing an integral up to each previous search pointer to a search pointer file at a sector, and calculating an integral up to a target search pointer in the sectors in conducting a search to obtain an address of a compressed audio file.
Compressed data equal in size can often be reproduced over different periods of time. This is because data having different amounts of information are compressed at different compression ratios (or bit rates).
For example in a specification for storing audio information to a DVD (i.e., a DVD audio specification) packed pulse code modulation (packed PCM) is supported as a form for compressed data. Packed PCM is a form of compressed data capable of maintaining the same quality as linear PCM numerically representing (or sampling) sound at constant temporal intervals and recording it.
If such compressed data is reproduced, and each packet's reproduction time is equal and a packet reproduced when reproduction starts is determined, there is a possibility that an offset (or error) is introduced between the user's desired reproduction portion and an actually reproduced portion. Although it depends on compressed data to be reproduced, this error is for example approximately five seconds. As the error is introduced, the user cannot reproduce music, video or the like at his/her designated point, and thus feels inconvenient and/or unsatisfied when he/she utilizes the reproduction apparatus.
The above disadvantage will be described with reference to a specific example. A reproduction apparatus has an “AB repeat function”. When information's reproduction start and end time points (points A and B, respectively) are designated, the function repeatedly reproduces the information between points A and B.
For example, a user who desires to attain proficiency in spoken English may utilize the AB repeat function to repeatedly reproduce a sentence. The user determines start and end time points corresponding to a portion to be repeatedly reproduced, and designates points A and B.
When the AB repeat function is effected, the reproduction apparatus starts to reproduce the information at point A and when the reproduction apparatus reproduces the information up to point B the reproduction apparatus returns to point A for reproduction. The reproduction apparatus searches for and reproduces the compressed data corresponding to the reproduction start time point designated as point A. However, a reproduction time point as recorded in a time stamp can be different from that designated by the user. In that case, the apparatus starts to reproduce data at a point different from the reproduction start position designated by the user.
In particular, a reproduction start point determined by the apparatus is offset from a point designated by the user, the AB repeat function starts to reproduce information at an offset point for each reproduction. Accordingly, the user needs to handle it for example by redesignating point A, and will thus feel inconvenient and/or satisfied with the reproduction apparatus's performance.
If a time stamp is read from a packet having a time stamp (PTS) included therein and a packet that is reproduced at a time point closest to a designated time point is determined, the error between the designated time point and the stamp can be reduced. If a process is performed that reads a time stamp, for example in order of reproduction, from a packet including a time stamp, however, the process requires time and will compel the user to wait until the reproduction apparatus starts to reproduce information.